Vehicles to be towed behind other vehicles (trailers) are not new, and in the past these non-motorized vehicles have generally been towed by a one-point ball and socket hitch, with two or more wheels under the trailer. This provided a very satisfactory towing arrangement for turning and also for passing over bumps or obstacles, but it was extremely difficult to move in a rearward direction (backup), especially by a person not experienced in handling towable vehicles.
Many years ago a trailer was developed which had a two-bar attachment to the towing vehicle, with a single wheel in the center of the trailer. That wheel was pivotable and inasmuch as the trailer was attached at two points, a backing-up operation could be performed because the trailer wheel pivoted and the trailer was pushed backward following the precise movement or direction of the vehicle. Quite often the two-point attachment to the towing vehicle was by clamps affixed to the bumpers.
However, the big disadvantage of such a trailer was that the one-point contact with the ground, i.e., the single pivotable wheel, caused great instability for heavy loads which extended sidewards and outwardly beyond the single wheel. Frequently the trailer would twist on the tow bars, and the entire trailer would collapse in a sideward direction. Because the forces were directed to the bumper, the bumper would also be damaged.
Thus it can be seen that a trailer with one pivotable wheel, and a rigid two-bar hitch arrangement is not new, but the disadvantages of such equipment are evident.